Method for Cleaning Metal or Metal Alloy Surfaces

ABSTRACT

A method for cleaning a surface of a metal or metal alloy body by immersing the surface in a basic aqueous electrolyte containing carbonate ions, and flowing DC current through the body to make the body anodic. After a time, the flow of DC current is stopped and the surface is removed from the electrolyte. The surface is then rinsed off to remove dirt, corrosion, coatings, and the like from the surface. The surface can then be dried and, if desired, coated for reuse of the body

RELATED APPLICATIONS

This application is a continuation-in-part of and claims priority from: our co-pending PCT Application PCT/US2016/045951 “Method for Cleaning Metal and Metal Alloy Surfaces” filed Aug. 8, 2016 at Attorney Docket No. 1-2310-PCT, co-pending PCT/US2014/060015 “Foundry Mixture And Related Methods For Casting And Cleaning Cast Metal Parts” filed Oct. 10, 2014 at Attorney Docket No. 1-2016-PCT, co-pending U.S. patent application Ser. No. 14/719,542 “Foundry Mixture And Related Methods For Casting And Cleaning Cast Metal Parts” filed May 22, 2015 at Attorney Docket No. 1-2016-DIV-A, and co-pending U.S. patent application Ser. No. 14/719,589 “Foundry Mixture And Related Methods For Casting And Cleaning Cast Metal Parts” filed May 22, 2015 at Attorney Docket No. 1-2016-DIV-B, the Ser. Nos. 14/719,542 and 14/719,589 applications each being a continuation in part of U.S. patent application Ser. No. 14/511,432 “Foundry Mixture And Related Methods For Casting And Cleaning Cast Metal Parts” filed Oct. 10, 2014 at Attorney Docket No. 1-2016 and now U.S. Pat. No. 9,038,708 that issued May 26, 2015, wherein applications PCT/US2014/060015 and Ser. No. 14/511,432 each further claim priority from expired provisional patent applications U.S. Patent Application No. 62/013,832 filed Jun. 18, 2014 at Attorney Docket No. 1-2016-P-2 and U.S. Patent Application 62/043,925 filed Aug. 29, 2014 at Attorney Docket No. 1-2016-P-3, the above-listed applications each incorporated by reference as if fully set forth herein.

FIELD OF THE DISCLOSURE

The disclosure relates generally to cleaning of metal or metal alloy surfaces, and more specifically, to electrolytic cleaning of metal or metal alloy surfaces.

BACKGROUND OF THE DISCLOSURE

Surfaces of metal bodies or components often must be cleaned for use. Cast metal bodies molded in a mold formed from a foundry mixture usually require cleaning before use to remove foundry mixture adhering to the as-cast surfaces.

Metal castings are cast in molds or receptacles formed from a conventional foundry mixture consisting of granulated foundry sand and a cured binder. The granulated sand takes the desired shape of the mold and the cured binder enables the granulated sand to retain the shape of the mold. The mold includes a shell defining a mold cavity. The mold may optionally include one or more cores placed in the mold cavity to define hollow elements or passages in the cast metal part, with the shell and cores defining the shape of the casting. Liquid metal is poured into the mold cavity and solidifies upon cooling to form the casting. The solid casting is then removed from the mold.

Some binders may include a binder material that is treated to hold or bond the refractory material within a rigid binder matrix. Other binders may include a compatible suspension agent along with the binder material that reacts with or otherwise cooperates with the binder material to hold or bond the foundry sand within a rigid binder matrix.

One type of binder includes a resin as the binder material and may utilize a suitable catalyst as the suspension agent. The resin cures to form a cured resin matrix. Resins commonly used as binder materials include (but are not limited to) urea formaldehyde (UF), phenol formaldehyde (PF) resins, and natural or synthetic gums.

Binders that form a cured resin matrix are referred to as “resin binders” herein. Resin binders may use a resin alone (that is, the resin binder does not include a suspension agent) or may include a resin and a catalyst as suspension agent.

The resin may be a thermosetting resin or heat-cured resin that cures or cross-links when heated, or the resin may require the presence of a catalyst to induce curing or cross-linking of the resin. When the foundry mixture is formed, the resin is treated to cure the resin. Specific resins use different types of treatment to form the matrix. “Hot-box”, “cold-box”, and “no-bake” are examples of different treatment types.

Hot-box treatment utilizes pre-heating the foundry mixture with a thermosetting resin binder. The foundry mixture is typically heated to temperatures between about 35 degrees Centigrade and about 300 degrees Centigrade to cure the resin. Resins used in hot-box treatment may include furan resins and furfuryl alcohols. Typically the resins are cured in the presence of a latent acid curing catalyst.

Cold-box treatment utilizes passing a vapor or gas catalyst through the foundry mixture to induce curing of the resin. The resin used is typically a phenolic urethane. A gaseous tertiary amine curing catalyst is passed through the shaped sand and resin mixture to cure the mixture. The catalyst may be TEA (tetraethylamine) and DMEA (dimethylethylamine). The sand and resin mixture may be shaped in a pattern and allowed to cure and become self-supporting to form the mold.

No-bake treatment utilizes a catalyst added directly to the resin that cures the resin at ambient temperatures without the need for baking. The resin used is typically a phenolic urethane. The suspension agent includes a solvent that reacts with a liquid curing catalyst mixed with the sand and resin before shaping. The foundry mixture typically cures 30 minutes to a few hours after mixing in the solvent.

Binders that do not utilize a resin are referred to as “non-resin binders” herein.

Some types of non-resin binders utilize water or some other liquid (such as vegetable oil, marine oil, or other liquids known in the art) as a suspension agent that binds the binder material together. Non-resin binders that utilize water or other liquid as a suspension agent are referred to as “liquid cured binders” herein. Liquid cured binders that utilize water as a suspension agent are referred to as “aqueous binders” herein, while binders that do not utilize water as a suspension agent are referred to as “non-aqueous binders” herein. Resin binders that are heat cured or catalyst cured, for example, are non-aqueous binders.

Some types of aqueous binders include clays (such as bentonite or kaolinite) or other solid mineral agent as the binder material. The sand, mineral agent, and water are mixed together. There is sufficient water and time after mixing to hydrate the binder material and form a mortar. The mortar dries and becomes rigid, thereby holding the sand within a mortar matrix.

Some aqueous binders utilize calcium oxide, CaO, as a precursor binder material. The calcium oxide reacts with the water suspension agent to form a calcium hydroxide mortar. There is effectively no calcium oxide in the foundry mixture after the calcium oxide has hydrated and the binder has cured.

Some types of binders include a non-resin binder material that is cured by heating. Such binders are referred to as heat-cured non-resin binders herein.

One type of heat-cured non-resin binder includes inorganic clay components such as aluminum silicate, bentonite, or montmorillonite as a binder material. In embodiments the clay is heated to form a clay binder matrix that holds the sand within the clay matrix.

Yet other types of non-resin binders include sodium silicate as a binder material.

Binders in a foundry mix in which the binder material has been treated to form the binder matrix are referred to as “cured binders” herein. Cured binders include cured resin binders in which the resin has been cured by heating or by catalyst reaction to form a resin binder matrix, cured liquid cured binders in which the binder material has been mixed with a liquid and reacts to form a cured binder matrix, and heat-cured binders in which the binder material has been heated to form a cured binder matrix.

The foundry mixture may also optionally include additional material or materials to improve the finish of casting surfaces, the dry strength of the mold, refractoriness, and “cushioning” (the creation of voids in the mold that enable the mold to expand when metal is poured into the mold), or to provide other desirable characteristics in the finished mold.

Typically, up to 5% of reducing agents, such as coal powder, pitch, creosote, and fuel oil, may be added to the foundry mixture to prevent wetting (liquid metal sticking to sand particles, thereby leaving sand particles on the casting surface), improve surface finish, decrease metal penetration, and burn-on defects. These additives achieve this by creating gases at the surface of the mold cavity, which prevent the liquid metal from adhering to the sand.

Typically, up to 3% of “cushioning material”, such as wood flour, saw dust, powdered husks, peat, and straw, can be added to the foundry mixture to reduce scabbing, hot tear, and hot crack casting defects when casting high temperature metals. These materials burn-off when the metal is poured, thereby creating voids in the mold that allow the mold to expand.

Typically, up to 2% of cereal binders, such as dextrin, starch, sulphite lye, and molasses, can be used in the foundry mixture to increase dry strength (the strength of the mold after curing) and improve surface finish. Cereal binders also improve collapsibility and reduce shakeout time because they burn-off when the metal is poured.

Typically, up to 2% of iron oxide powder can be used in the foundry mixture to prevent mold cracking and metal penetration, essentially improving refractoriness. Silica flour (fine silica) and zircon flour may also improve refractoriness.

Material or materials added to the foundry mixture to improve the finish of casting surfaces, the dry strength of the mold, refractoriness, and/or cushioning are referred to as “additives” herein.

After casting, sand and binder still adhering to casting surfaces are typically removed by mechanical agitation of the casting, shot blasting, or other mechanical cleaning methods. Alternatively, the casting may be dipped into a molten bath.

Used sand cleaned from the casting has economic value. Used foundry sand is, for example, used as a fine aggregate in making concrete.

It is known to remove contaminants from surfaces of metal or metal alloy bodies using electrolysis. The surface to be cleaned is wetted by the electrolyte and DC current is passed through the body acting as a cathode in the electrolyte. The inventors' U.S. Pat. No. 6,203,691 fully incorporated herein by reference discloses methods of cleaning metal bodies using a basic aqueous electrolyte containing disodium phosphate and sodium bicarbonate. The cleaning methods disclosed in the '691 patent, although well-suited for many cleaning needs, do not efficiently remove foundry mixtures, powder coatings or other specialized coatings found on metal bodies.

Removal of foundry mixtures from cast metal bodies is often difficult and time consuming. Electrolytic cleaning of cast metal bodies has been employed for more efficient cleaning.

Hathaway US Patent Application Publications 20050087323 and 20050087321 each disclose a foundry mixture that includes sand, a resin binder, and a disintegration additive that reportedly assists in removing the foundry mixture from casting surfaces. The casting is electrolytically cleaned after being removed from the mold. The disintegration additive assists during the electrolytic cleaning in removing the remaining foundry mixture adhering to casting surfaces.

The disintegration additive is a salt that is preferably inorganic and soluble in water. Preferred embodiments of the mixture include disintegration additives having relatively high melting points (above 300 degrees C., which is much lower than the melting points of common cast metals such as iron, steel, titanium, or aluminum).

Specific examples of disintegration additives are given in paragraph 22 of the '323 publication. Preferred anions for the salt of the disintegration additives include carbonates, nitrates, sulfates, phosphates, hydroxides, and halogens. Certain preferred salts include cations of sodium, potassium, calcium, ammonium, or magnesium, and include salts, such as for example: sodium carbonate, sodium bicarbonate, sodium chloride, sodium hydroxide, sodium iodide, sodium nitrate, sodium phosphate, disodium phosphate, sodium sulfate, potassium carbonate, potassium chloride, potassium hydroxide, potassium iodide, potassium nitrate, potassium phosphate, potassium sulfate, calcium carbonate, calcium chloride, calcium hydroxide, calcium iodide, calcium nitrate, calcium sulfate, ammonium sulfate, ammonium carbonate, magnesium carbonate, magnesium chloride, magnesium hydroxide, magnesium iodide, magnesium nitrate, magnesium phosphate, magnesium sulfate, and equivalents and mixtures thereof. The disintegration additive may be selected from the group consisting of sodium chloride, potassium chloride, sodium carbonate, sodium bicarbonate, sodium phosphate, and mixtures thereof. The disintegration additive may comprise sodium chloride. The disintegration additive may comprise sodium bicarbonate, disodium phosphate, and mixtures thereof. The disintegration additive may comprises sodium carbonate, disodium phosphate, and mixtures thereof.

Hathaway discloses in embodiments that the disintegration additive reportedly enhances the electron ion conduction of the casting when contacted with a polar electrolyte such as water. Water soluble salts would be suitable for such disintegration agents.

Hathaway discloses in other embodiments that the disintegration additive volatilizes during casting of the metal part, leaving behind a porous and slightly unstable mold structure. Hence, the melting point of such disintegration agents must be below the melting point of the metal being cast.

It has been found, however, that volatizing the disintegration additive during casting may adversely impact mold strength, and may adversely impact the finish of the casting surfaces. Furthermore, some disintegration additives include sodium that impairs the economic value of used, recovered sand. The sodium contaminates the used sand, making the sand unsuitable as a fine aggregate in concrete.

Even after initial cleaning when new, metal bodies often must be returned to a clean, bare metal surface for recycling and reuse. Metal alloy wheels of trucks and airplanes, for example, may be sold with a powder coating on wheel surfaces. Powder coating is a thermoplastic or polymer coating that creates a hard finish that is tougher than conventional paints. The powder coating is applied electrostatically to the surface and then cured to form a protective skin over the surface. The powder coating, along with brake dust, road grime, oil, and other surface contaminants or coatings must be removed from the wheel before the wheel can be reused.

Conventional methods to remove coatings from the surfaces of metal or metal alloy bodies include use of specific solvents, heating the body to high temperatures, or abrasive blasting. These conventional methods have disadvantages. Some solvents are suspected carcinogens. Heating components to high temperatures may cause warping or may adversely impact heat treatments of metal alloys. Abrasive blasting may remove metal as well as damage or roughen the surface. And conventional cleaning methods either take a long time to remove specific types of coating or require extensive manual labor and handling.

Thus there is a need for an improved method to clean surfaces of metal or metal alloy bodies that can remove foundry mixtures, powder coatings and other surface coatings or contaminants.

SUMMARY OF THE DISCLOSURE

Disclosed is a method for electrolytic cleaning of surfaces of metal components or bodies well suited for removing foundry mixtures, powder coatings, and other surface coatings and contaminants. The electrolyte used in possible embodiments of the disclosed method is inexpensive, environmentally friendly, and non-hazardous.

A method for cleaning a metal surface of a metal or metal alloy body in accordance with the present disclosure includes the steps of:

(a) wetting the surface of the body with an aqueous electrolyte, the electrolyte comprising a dissolved carbonate salt and having a pH greater than 7;

(b) making the body anodic by flowing DC current through the body concurrently with step (a), the flow of DC current sufficient to thereby coat the wetted surface with a coating of additional material; and

(c) stopping the flow of the DC current after performing step (b) and removing the additional coating from the surface, thereby cleaning the surface.

The surface of the body in embodiments of the disclosed method can be wetted by immersing the body in the electrolyte or by spraying the body with the electrolyte.

Contaminants or coatings that can be cleaned from surfaces of metal or metal alloy bodies in accordance with the disclosed method include, but are not limited to, carbonization, surface powder coatings, paints, petroleum based or hydrocarbon (organic) based materials, environmental contaminants including dirt, soil, dust, or smut.

The inventors have found that applying a DC current making the body anodic deposits a coating of an additional material on the portion of the body wetted by the electrolyte. Without being bound by or limited to any theory or explanation, the inventors herein theorize as to the creation and cleaning benefits of the additional material coating. The additional material is not believed to be generated by either reduction or oxidation of metal or metal compounds forming the body but is believed to be created by oxidation of the carbonate ions in the electrolyte. The oxidized carbonate ions form the coating on the portion of the body immersed in or wetted by the electrolyte. The additional material coating is visible as a substantially gray to black coating that covers the entire outer surface of the portion of the body immersed in or wetted by the electrolyte. The additional material coating appears to physically or chemically break down coatings and contaminants (including but not limited to powder coatings) that are on the immersed or wetted surfaces without harming the body, and without removing or otherwise affecting metal or metal alloys of the body.

The electrolyte also darkens with creation of the additional material, but the darkening of the electrolyte does not appear to adversely impact the cleaning process.

After removal from the electrolyte, the additional material coating can be rinsed off with water. Rinsing off the additional material also removes the contaminants on the immersed surfaces (including powder coatings if present), resulting in clean surfaces suitable for recycling.

In a possible embodiment of the disclosed method, a low pressure water jet is used to rinse off the additional material. “Low pressure water jet” as used herein means use of a water jet in which the pump pressure is less than 5,000 psi (340 bar). Rinsing using a low pressure water jet of about 2,000 psi has been found effective in embodiments of the disclosed method in removing the additional coating and, along with the additional coating, powder coatings and other contaminants without damage to the body.

The carbonate salt must be dissolvable in water. Preferred carbonate salts are potassium carbonate and sodium carbonate, the most preferred is potassium carbonate.

The electrolyte is a basic electrolyte. The electrolyte in embodiments may be mildly alkaline or may be highly alkaline. The electrolyte in embodiment may have a pH greater than 7, or a pH from greater than about 8 to not more than about 13, or a pH of about 11.

The electrolyte may be maintained at a temperature not less than about 70 degrees Fahrenheit to not more than the boiling point of the electrolyte, or may be maintained at between not less than about 150 degrees Fahrenheit and the boiling point of the electrolyte.

The DC current applied to the body in embodiments may be about 200 amperes or greater, may be between about 200 amperes and about 5000 amperes, and may be about 1000 amperes.

The DC current applied to the body in embodiments may be applied for between about 2 minutes and about 15 minutes, may be applied for between about 3 minutes to about 5 minutes, and may be applied for about 5 minutes.

The DC voltage applied to the body to induce current flow in embodiments may be less than or equal to about 200 volts, and the applied DC voltage may be equal to or more than about 3 volts.

The additional material may be rinsed off the body in embodiments no more than about 15 minutes after removal from the electrolyte, and is preferably rinsed off not more than about 10 minutes after removal from the electrolyte, and most preferably is rinsed off not more than about 5 minutes after removal from the electrolyte.

It has been observed that the additional material coating hardens after removal from the electrolyte and after time may become so hard that it becomes relatively difficult to remove. The sooner after the body is removed from the electrolyte that the body is rinsed to remove the additional material, the easier it is to remove the additional material. In an embodiment of the disclosed method a low pressure water jet has been found effective for removing the additional material and contaminants if the rinse is started within about 15 minutes after stopping the DC current.

A suitable source of DC current for use in embodiments of the disclosed methods includes, but is not limited to, the Model No. 43pl-00 im-048 rectifier manufactured by Process Electronics Corp, Mt Holly, N.C. 28120 USA. This rectifier can provide 1000 DC amperes at 48 amperes with a continuous duty cycle.

Powder coatings have been successfully removed from motor vehicle wheel hubs and rims made from aluminum alloy, steel, and manganese alloys. Other bodies that have been successfully cleaned using the disclosed methods include cast iron and stainless steel bodies.

In an additional embodiment of the disclosed method, the electrolyte includes trisodium phosphate (“TSP”, Na₃PO₄). TSP is used in the formulation of soaps, detergents, and other cleaning agents, and was commonly used in household cleaning products. But use of TSP for cleaning metal fixtures was not recommended because the TSP could stain the metal.

The addition of trisodium phosphate to the electrolyte maintains the basic pH of the electrolyte, and if present in sufficient concentration, results in the cleaned metal part having a brighter finish as compared to cleaning without TSP. No staining of metal parts cleaned with electrolyte containing TSP was noted.

In a further embodiment of the disclosed method used for cleaning foundry mixture from cast metal bodies, a foundry mixture for foundry casting for use in making at least a portion of a mold for a cast part includes a granular refractory material, a binder, optional additives, and a cleaning agent. In embodiments the binder may be a resin binder, a non-resin binder, a liquid cured binder, or a heat cured binder material.

The cleaning agent is calcium oxide (CaO). The calcium oxide is added and mixed with the granular refractory material, binder, and optional additives to form a foundry mixture. The calcium oxide may be added to the foundry mixture in a finely ground or powdered form. In embodiments the ground or powdered calcium oxide may have a fineness of between about 100 mesh to about 500 mesh, which corresponds to a particle size of between about 0.0059 inches and about 0.001 inches.

The calcium oxide may, in possible embodiments of the foundry mixture, be between about one-half percent (½%) and about five percent (5%) by weight or by volume of the weight or volume of the refractory material n the foundry mixture. The calcium oxide, may, in possible embodiments of the foundry mixture, be between about one-half percent (½%) and about five percent (5%) by weight or by volume of the sum of the weight or volume of the refractory material and the binder in the foundry mixture. Other embodiments may use more or less calcium oxide.

Calcium oxide as a cleaning agent in a foundry mixture that contains a cured binder forms a solid mold capable of accepting molten metal for casting. The calcium oxide does not form part of the cured binder, that is, the calcium oxide has not reacted with the binder material to cure the binder. Like the refractory material, the calcium oxide will be held and distributed within the binder matrix like the refractory material.

Calcium oxide is not a salt and is essentially insoluble in water. Calcium oxide has a melting point of 2,572 degrees Centigrade, substantially higher than the melting points of aluminum, brass, bronze, iron, copper, gold, lead, magnesium, nickel, silver, steel, tungsten, zinc, and other commonly cast metals. The calcium oxide does not vaporize during casting and so maintains good surface quality of the casting and does not produce an unstable mold structure.

Calcium oxide as used in the disclosed foundry mixture as a cleaning agent is not a disintegrating agent as defined by Hayword: the calcium oxide does not vaporize during casting of the metal part and so casting does not form a porous and unstable mold structure, and the calcium oxide does not enhance the electron ion conduction of the casting when contacted with a polar electrolyte such as water.

The cleaning agent results in more efficient electrolytic cleaning of a residual foundry mixture from a metal casting. The exact mechanism by which the cleaning agent is not known, and any speculation as to the cleaning mechanism is not intended to be limiting in any way.

Calcium oxide in particular is inexpensive and is widely available. Calcium oxide is compatible with the manufacture of concrete and so the presence of calcium oxide in the binder does not adversely impact the economic value of the used foundry sand.

If the foundry mixture has not yet been cured to enable the refractory material to retain a desired shape, the binder may include only a binder material. If the foundry mixture has been cured, the binder material may include a suspension agent that has reacted with the binder material.

By “optional additives” it is meant that the foundry mixture may contain one or more additives or may contain no additives.

In an embodiment, the foundry mixture includes a granular refractory material, a non-aqueous binder, optional additives, and a cleaning agent.

The granular refractory material may be foundry sand.

Also disclosed is a foundry mold formed for the casting of a part that includes granular refractory material, a cured binder, optional additives, and a cleaning agent. In embodiments the cured binder may be a cured resin binder, a cured non-resin binder, a cured liquid cured binder, or a cured heat cured binder. The cured binder may or may not include a suspension agent.

Also disclosed is a method of forming a casting that includes the steps of pouring molten metal into a mold, the mold being formed of a foundry mixture that includes a granular refractory material, a cured binder, optional additives, and a cleaning agent. The cured binder may be a cured resin binder, a cured non-resin binder, a cured liquid cured binder, or a cured heat cured binder. The cured binder may or may not include a suspension agent. The molten metal is cooled to form a solid casting in the mold, and the solid casting is removed from the mold.

Also disclosed is a method of forming a casting that includes the steps of pouring molten metal into a mold, the mold being formed of a foundry mixture that includes a granular refractory material, a cured binder, optional additives, and a cleaning agent. The cured binder may be a cured resin binder, a cured non-resin binder, a cured liquid cured binder, or a cured heat cured binder. The cured binder may or may not include a suspension agent. The molten metal is cooled to form a solid casting in the mold, and the solid casting is removed from the mold.

Also disclosed is a method for removing residual foundry mixture from a metal casting wherein the method includes the steps of: electrolytically cleaning a cast metal part, the foundry mixture including a granular refractory material, a cured binder, optional additives, and a cleaning agent. The cured binder may be a cured resin binder, a cured non-resin binder, a cured liquid cured binder, or a cured heat cured binder. The cured binder may or may not include a suspension agent.

Also disclosed is a method for removing a residual foundry mixture from a metal casting wherein the method includes the steps of: electrolytically cleaning a cast metal part, the foundry mixture including a granular refractory material, a cured binder, optional additives, and a cleaning agent. The cured binder may be a cured resin binder, a cured non-resin binder, a cured liquid cured binder, or a cured heat cured binder. The cured binder may or may not include a suspension agent.

An embodiment of the step of electrolytically cleaning the cast metal part includes the step of attaching the metal casting having residual foundry mixture to a power source having a first and a second electrode of opposite polarities, wherein the first electrode is attached to the metal casting. The metal casting is immersed in or otherwise wetted by an electrolyte that is in contact with the second electrode. Current is generated through the electrolyte, from the first electrode to the second electrode.

In an embodiment the electrolyte is an alkaline electrolyte. The electrolyte may be formed by mixing potassium carbonate with water. The electrolyte may have a pH of about 12 or greater.

The disclosed method for cleaning has a number of advantages. Potassium carbonate and sodium carbonate electrolytes are inexpensive and environmentally friendly. Food grade potassium carbonate and food grade sodium carbonate are available and are non-toxic. Rinsing the bodies to remove the additional coating and contaminants can be automated, is not labor intensive, and can generate high production rates of cleaned bodies as compared to conventional cleaning methods (particularly when removing powder coatings).

A further advantage of the disclosed method for cleaning when cleaning aluminum or aluminum alloy bodies is that the body is not discolored after cleaning. Conventional cleaning of aluminum or aluminum alloy bodies in a strong alkaline solution may discolor the body. Rubin et al. U.S. Pat. No. 4,457,332 for example suggests adding metasilicate salt to a strongly basic aqueous solution to avoid discoloration of aluminum bodies. The inventors have found that soft metal or metal alloy bodies such as aluminum and aluminum alloy bodies cleaned in accordance with the disclosed method do not discolor even when cleaned using a highly alkaline aqueous electrolyte formed by carbonate salts.

Further areas of applicability of the disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating specific disclosed embodiments, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

Other objects and features of the disclosure will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing sheets illustrating one or more illustrative embodiments.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 is a schematic view of a metal alloy wheel immersed in an electrolyte for cleaning in accordance with an embodiment of the disclosed method of cleaning.

FIG. 2 is an enlarged view of a portion of the wheel shown in FIG. 1.

FIG. 3 schematically illustrates a first embodiment device useful in cleaning cast metal parts that are cast utilizing the disclosed foundry mixture.

FIG. 4 schematically illustrates a second embodiment device useful in cleaning cast metal parts that are cast utilizing the disclosed foundry mixture.

DETAILED DESCRIPTION

FIG. 1 illustrates a used truck or airplane wheel 10 totally immersed in an electrolyte 12 for cleaning in accordance with the disclosed method. The wheel 10 is a conventional aluminum alloy wheel that has a powder coating 14 on an external surface 16 of the wheel. See FIG. 2. It is desired to remove the powder coating 14 and surface contaminants 18 on the powder coating from the surface 16 to enable recycling and reuse of the wheel.

The wheel 10 is connected electrically in series to an anode terminal 20 of a DC current source 22 by a conductor 24. A steel or iron cathode 26 is also immersed in the electrolyte 12 and is connected in series to a cathode terminal 28 of the current source 22 by a conductor 30. The wheel 10 and the cathode 26 are electrically connected by the electrolyte 12.

The illustrated electrolyte 12 is an aqueous basic electrolyte formed by dissolving potassium carbonate (K₂CO₃) in water. The potassium carbonate is preferably food-grade potassium carbonate.

The pH of the electrolyte is about 11. The temperature of the electrolyte is about 130 degrees Fahrenheit.

In the illustrated embodiment the wheel 10 is immersed into a 200 gallon bath of electrolyte 12.

The DC current source 18 is energized and flows 1000 amperes of DC current from the anode terminal 16, through the wheel 10 and to the cathode 26, and back to the cathode terminal 22. The impressed DC current makes the wheel 10 anodic, that is, anodic with respect to the electrolyte 12.

The current source 18 is energized and supplies the 1000 ampere current through the wheel 10 continuously for five minutes. The current source 18 is then shut off and the wheel 10 is removed from the electrolyte 12.

While the DC current is flowing through the wheel 10, an additional layer of material is deposited on wetted surfaces of the wheel 10. The electrolyte 12 also darkens. It has been found that the wheel 10 does not appreciably heat while the DC current is flowing. It may even be necessary to heat the electrolyte 12 to maintain a desired electrolyte temperature while the DC current is flowing.

In the illustrated embodiment it is not necessary to treat the electrolyte in response to the electrolyte darkening. Additional potassium carbonate and/or water may be added to the electrolyte to maintain the desired pH. The electrolyte may be filtered in a conventional manner to remove dirt, soil, or other contaminants introduced into the electrolyte by the bodies being cleaned.

After the current source 18 is shut off, the wheel 10 is removed from the electrolyte 12. The wheel 10 is rinsed with a low pressure water jet spray to remove the additional material deposited on the wheel 10. In the illustrated embodiment the wheel 10 is sprayed with a 2000 psi water jet spray not more than 5 minutes after removal of the wheel from the electrolyte.

The jet spray also removes the powder coating 14 and the contaminants 18 from the wheel surface 16. After rinsing, the wheel 10 has a clean wheel surface 16 capable of accepting application of a new powder coating and/or alternative surface coatings.

After rinsing, the wheel 10 is dried. The wheel 10 may then be powder coated or otherwise coated or painted for return to the aftermarket and reuse.

In alternative embodiments of the disclosed method, some, but not all, surfaces of the metal or metal alloy body require cleaning. In such embodiments, the body may only be partially immersed in the electrolyte 12 if total immersion is not required to wet the surfaces to be cleaned.

In other alternative embodiments of the disclosed method, surfaces to be cleaned may be wetted by spraying electrolyte on the surfaces to be cleaned. The electrolyte spray must electrically connect the body as anode with the cathode and must conduct sufficient DC current to create the additional material coating.

In a further alternative embodiment of the disclosed method, TSP was added to the potassium carbonate based electrolyte and wheels similar to the wheels 10 were cleaned using different concentrations of trisodium phosphate in the electrolyte.

A TSP concentration of 1% or less (calculated as the weight of TSP divided by the weight of the potassium carbonate in the electrolyte and expressed as a percentage) had no appreciate effect on the cleaning of the wheel.

A TSP concentration of 5% had a positive effect, increasing the shine of the cleaned wheel, but the shine would not be considered very bright.

A TSP concentration of 50% resulted in good brightness of the cleaned wheel.

A TSP concentration of 100% (equal weights of TSP and potassium carbonate) had the best brightness.

It is contemplated that bodies may be cleaned by automating the disclosed method. For a nonlimiting example, metal or metal alloy bodies to be cleaned may be conveyed to an electrolysis station for immersion in or wetting with the electrolyte and application of DC current. Application of the DC current may stop after a predetermined time, or if a computerized optical monitoring system determines that the surface of the body has been adequately coated with the additional material to end application of DC current.

After the application of DC current stops, the body is moved from the electrolysis station to a rinse station for rinsing. The electrolyte is continuously filtered to remove contaminants in the electrolyte. The pH, temperature, and volume of electrolyte is monitored and maintained within predetermined limits by an automatic control system (not shown).

Also disclosed is a foundry mixture usable for forming a casting mold and/or a core for use with a casting mold for casting ferrous and non-ferrous metal parts, including metal parts made from aluminum, brass, bronze, iron, copper, gold, lead, magnesium, nickel, silver, steel, tungsten, zinc, and the like. The foundry mixture is cured to form a mold shell and/or mold core for foundry molding of the cast metal part.

The foundry mixture consists of a granular refractory material, a binder material, a cleaning agent, and may optionally include additives. The mixture may of course include impurities included with the addition of the materials forming the foundry mixture, but such impurities are not considered as forming a part of the foundry mixture.

The granular or particulate refractory material may be, in alternative embodiments, a sand formed from one or more of silica, olivine, chromite, zircon, and chamotte. Other sands conventionally used in foundry casting may also be used, including bank sands and synthetic sands. The sand may be coarse-grained sand, fine-grained sand, or be a mixture thereof.

The binder material may be a resin binder material, a non-resin binder material, a liquid cured binder material, a heat cured binder material,

The binder material may in embodiments be part of a resin binder that includes a resin as the binder material and may optionally include a suspension agent. Resins, in embodiments, may be (but are not limited to) urea formaldehyde (UF) resins, phenol formaldehyde (PF) resins, natural or synthetic gums, furan resins and furfuryl alcohols.

The resin binder material in embodiments may be a heat-curable resin in which heating the foundry mixture cures the resin to form a heat-cured resin binder. The resin binder in other embodiments may require a catalyst as a suspension agent. The catalyst when added to the foundry mixture reacts with the resin and cures the resin to form a cured resin binder.

The cleaning agent includes calcium oxide (CaO). The calcium oxide may, in embodiments, be obtained from limestone that is preferably 99% (ninety-nine percent) or more calcium oxide. The calcium oxide is preferably provided in powdered or finely ground form for use in preparing the disclosed foundry mixture. The cleaning agent in embodiments may consist only of calcium oxide.

The refractory material and the binder material (and the suspension agent if present) together form a first portion of the disclosed foundry mixture. The calcium oxide may in embodiments of the disclosed foundry mixture be present in the foundry mixture by weight or by volume between about ½% (one-half percent) and about 5% (five percent) of the first portion of the foundry mixture.

The following working example is given as an illustration only and is not intended to limit the scope of the disclosure. The results of tensile strength testing and loss on ignition testing for an embodiment of the disclosed foundry mixture are given below.

A sample of a foundry mixture that includes two-and-one-half percent (2½%) resin coated sand was mixed with one-half percent (½%) by weight finely ground calcium oxide. The foundry mixture was then formed into standard specimen “biscuits” used for the tensile testing of foundry mixtures. The e biscuits were then cured and allowed to cool to room temperature. The average cold tensile strength of the biscuits was four hundred and forty-five (445) pounds per square inch. The average Loss on Ignition was two and sixty-nine hundredths percent (2.69%). Recommended values for a conventional 2½% resin mixture is a minimum cold tensile strength of 420 pounds per square inch and a Loss on Ignition of between two and sixty hundredths percent (2.60%) and two and ninety hundredths percent (2.90%).

In use for foundry casting, the foundry mixture is formed into at least a portion of a mold, and may also be used in forming one or more cores that are included as part of the mold for defining the shape of a cast part. The foundry mixture forming the mold and the one or more cores is cured to form a rigid matrix encapsulating the refractory material and capable of retaining the shape of the mold or core when the mold is being used to mold the molten metal. The molten metal flows into the mold and solidifies in the mold to form the cast metal part.

The type of ferrous or non-ferrous metal being cast, the alloys in the metal, the desired surface quality of the finished part, and other factors influence the selection of refractory material, binder, binder curing methods, and additives to be used in casting a specific metallic part as is known in the metal casting art and so will not be described in further detail herein.

The disclosed foundry mixture may be distributed in pre-mixed, pre-measured form in which the cleaning agent, refractory material, and binder are mixed together for convenience prior to use. If the binder material requires a suspension agent that is not compatible with a pre-mixed foundry mixture (that is, adding the suspension agent would start immediate curing of the binder material or would react or hydrate the calcium oxide cleaning agent), the pre-mixed mixture may be provided without a suspension agent (that is, with binder material only). The components may be mixed together using conventional high speed continuous mixers, low-speed augur-type continuous mixers, batch mixers. or other conventional mixing devices or mixing methods.

The shaping and curing of the disclosed foundry mixture to form a mold shell or core defining the desired shape of the casting produced by pouring melted metal into the mold, the formation of sprues, runners, and risers to flow molten material to and within the mold, including pattern making, lost wax casting, and other variations of shaping and curing a foundry mixture to achieve the desired shape of the casting are known in the foundry casting art and so will not be described in further detail herein.

After the molten metal cools and solidifies, the cast metal part is removed from the mold. Inner cores may remain in the removed part, and residual foundry mixture may adhere to casting surfaces.

FIG. 3 illustrates a cast metal part 110 formed by flowing molten (liquid) metal into a mold formed from the disclosed foundry mix. The illustrated foundry mixture includes a resin binder and calcium oxide as the sole cleaning agent. The part 110 is immersed in an electrolyzer 112 for removing cores or residual foundry mixture that includes the cleaning agent 113 from the cast metal part 110. The illustrated cast metal part 110 is a steel part. The electrolyzer 112 includes a nonmetallic container or vat 114 holding a liquid electrolyte 116, one or two cathodes 118, a power supply or current source 120, and an anode contact 122. The electrolyte 16 is a basic (alkaline) electrolyte. As shown in FIG. 3, the cast part 110 is immersed into the electrolyte 116 and is held in the electrolyte by a holder 123. The cast part 110 is connected to the anode contact 122. The cathodes 118 are connected to the positive output terminal 124 of the source 120. The anode contact 122 is connected to the negative output terminal 26 of the source 120.

Electrolyte 116 is an aqueous basic solution that, in the illustrated embodiment, is made of a mixture of water and potassium carbonate. The electrolyte 116 has a pH of 12, but in other embodiments the pH may have a basic pH different than 112.

An alternative illustrative and non-limiting embodiment of the electrolyte is an aqueous basic solution made of a mixture of water and sodium bicarbonate. The alternative embodiment electrolyte has a pH of between about 8.5 and about 9.0, that is, the pH of the alternative embodiment electrolyte has a pH closer to 8.5 than to 8, and closer to 9.0 than 9.5.

In the illustrated embodiment, the cathodes 118 are made of stainless steel rods. The power supply 120 produces a low voltage direct current output from 5 to 350 DC amps output from a 60 HZ, 230 V, 3 phase alternating current source. Power supply 120 can be an Invertec V300-Pro power source manufactured by The Lincoln Electric Company of Cleveland, Ohio. Other power supplies and anodes may be used.

As shown in FIG. 3, the cast metal part 110 is totally immersed into electrolyte 116 and is connected as the positive terminal of the source 120. The source 120 is energized to flow current across the electrolyzer 112 for cleaning the cast metal part 110. During normal cleaning, the source 120 is energized for from 2 to 3 minutes per cast metal part, depending on the binder, metal composition, size of the part, and so on.

While the source 120 is energized, some materials removed from the cast part 110 float on the top of the electrolyte 116. Used foundry sand sinks to the bottom of the vat 114 and is later removed from the vat 114 and may be resold as a concrete aggregate. The sand and floating material are physically removed from the vat 114 by occasionally collecting each into separate containers.

After cleaning, the power supply 120 is deactivated. The cast metal part 110 is removed from the electrolyte 116 and disconnected from anode contact 122. After removal, the part 110 may be lightly rinsed with water. After rinsing, the cast part 110 has been cleaned and is ready for any post-cleaning procedure. For example, the part 110 may be dried and subsequently painted.

FIG. 3 illustrates a single cast metal part 110 immersed in the vat 114 for cleaning. However, a number of cast metal parts 110 in contact with each other can be immersed in electrolyzer 112 for simultaneous cleaning of the parts. One of the parts 110 is connected to the anode contact 122. The other parts 110 touch the part 110 connected to contact 122 or form a series of parts that contact one another and include the part 110 connected to the contact 22.

In an alternative embodiment the vat 114 is a stainless steel tank connected to the negative terminal 126 of the source 120 to form the anode of electrolyzer 12. The cast metal parts 110 would contact the vat 114 to be connected to the anode.

In other possible embodiments of the electrolyzer 112, the cast metal part 110 is connected to a power source having terminals of opposite polarities. The cast metal part 110 immersed in the electrolyte 16 is electrically connected to one terminal, and the electrolyte 16 is electrically connected to the other terminal for flowing electric current from the power source 120 through the cast metal part 110 for cleaning.

FIG. 4 illustrates an alternative method of cleaning the cast metal part 110 utilizing an industrial parts washer 128. Industrial parts washers typically include one or more processing zones for cleaning, rinsing, drying and other steps for cleaning cast metal parts. A conveyor typically transports the parts through the processing zones from one end of the washer to the other. Industrial parts washers typically spray the parts with liquid, and so most washers include an enclosure to capture the spray and contaminants being washed. Some industrial parts washers include a holder to secure and support the part to be washed. The holder and the part to be cleaned are enclosed in a chamber that forms a sealed unit encapsulating the part. A cleaner dispersing system is operable to remove residual materials from the part.

A continuous stream or spray 130 of electrolyte 116 is sprayed on the cast metal part 110 from a cathode 118 formed as a spray device. The metal part 110 is connected to a negative terminal 126 of the power source 120. The cast metal part 10 is secured by a holder 125 connected to the negative terminal 126 of the power source 120. In alternative embodiments each spray cathode 118 is submerged in a reservoir of electrolyte 116. A drain basin (not shown) collects the sprayed electrolyte and filters out the used sand for collection. Use of an industrial parts washer enables continuous, “production line” cleaning of cast metal parts as part of an industrial process that manufactures and cleans cast metal parts that are then sent downstream for further processing.

Non-limiting examples of casting and cleaning molded metal parts using the disclosed foundry mixture are described below.

A foundry mixture that includes sand, a clay binder, and five percent finely ground calcium oxide was formed into a mold and molten metal was poured into the mold to form a cast metal part. The mixture was mixed in a first set of trials with water to have about 4 percent moisture content and mixed in a second set of trials with water to have about 2 percent moisture content. Different types of sand (silica, chromite, zircon olivine, staurolite, graphite) were used in each set. The water was used as a suspension agent but did not react with the calcium oxide—the calcium oxide was added as the last ingredient to the foundry mixture shortly before pouring the molten metal into the mold and so the calcium oxide did not hydrate.

The resulting mold was not electrically conductive. Electrolytic cleaning of the cast metal part as described above effectively removed adhering foundry mixture.

In yet another set of tests, a foundry mixture suitable for cold-box treatment included from one percent to five percent calcium oxide by weight as a cleaning agent. Molds formed by the cold-box treatment were not electrically conductive.

In yet another set of tests, foundry mixtures containing inorganic and organic binders included from between one percent and five percent calcium oxide as a cleaning agent. Molds formed from the foundry mixtures were not electrically conductive. Electrolytic cleaning of the cast metal parts as described above effectively removed adhering foundry mixture. It was found that the calcium oxide did not affect the strength of the molds formed by the foundry mixtures as compared to equivalent foundry mixtures but without the calcium oxide cleaning agent.

In an additional set of tests, foundry mixtures containing amine resin and furane resin binders (and no appreciable amount of water) that included calcium oxide as a cleaning agent. Molds formed from the foundry mixtures were not electrically conductive. Electrolytic cleaning of the cast metal parts as described above effectively removed adhering foundry mixture.

In a further set of tests with resin binders that included calcium oxide as a cleaning agent, it was found that removing the same amount of sand from the conventional foundry mixture as the amount of calcium oxide cleaning agent being added did not adversely impact the strength of the molds formed from the foundry mixture.

In embodiments, the disclosed foundry mixture includes a liquid cured binder material and calcium oxide as a cleaning agent. The liquid cured binder material may be an aqueous binder material. Where the liquid suspension agent used may chemically react with the calcium oxide, the amount of suspension agent should be such that sufficient calcium oxide not forming part of the binder material remains after curing to act as a cleaning agent, or the calcium oxide should be added to the foundry mixture in a way that effectively prevents chemical reaction with the calcium oxide. For example, the calcium oxide can be added as a final ingredient to a foundry mixture containing up to 7 percent water shortly before molten metal is poured into a mold formed from the foundry mixture. The heat of the molten metal poured into the mold is well above the boiling point of water. The water in the foundry mixture cannot react with the calcium oxide.

Features recited in a claim may, in embodiments of the disclosed method, be found in combination with features recited in the claims.

While one or more embodiments have been disclosed and described in detail, it is understood that this is capable of modification and that the scope of the disclosure is not limited to the precise details set forth but includes modifications obvious to a person of ordinary skill in possession of this disclosure, including (but not limited to) changes in material selection, size, operating ranges (temperature, volume, displacement, stroke length, concentration, and the like), environment of use, and also such changes and alterations as fall within the purview of the following claims. 

What is claimed is:
 1. A method for cleaning a surface of a metal or metal alloy body, the method comprising the steps of: (a) wetting the surface of the body with an aqueous electrolyte, the electrolyte comprising a dissolved carbonate salt and having a pH greater than 7; (b) making the body anodic by flowing DC current through the body concurrently with step (a), the flow of DC current being not less than 200 amperes; and (c) stopping the flow of the DC current after flowing the DC current for not less than 2 minutes.
 2. The method of claim 1 wherein step (c) comprises rinsing the surface with water after stopping the flow of DC current.
 3. The method of claim 1 wherein step (b) comprises the step of flowing DC current for a sufficient length of time to coat the wetted surface with a coating of additional material.
 4. The method of claim 3 wherein step (c) comprises removing the coating of additional material from the body.
 5. The method of claim 1 wherein the electrolyte has a pH of between about 8 and about
 13. 6. The method of claim 5 wherein the electrolyte has a pH of about
 11. 7. The method of claim 1 wherein the carbonate salt comprises potassium carbonate.
 8. The method of claim 7 wherein the electrolyte comprises water and dissolved potassium carbonate.
 9. The method of claim 8 wherein the electrolyte comprises dissolved trisodium phosphate.
 10. The method of claim 9 wherein the trisodium phosphate is present in the electrolyte at a concentration of between 5% and 100% weight percent of the potassium carbonate.
 11. The method of claim 1 wherein step (b) comprises the step of: (e) flowing DC current of between about 200 amperes and about 5000 amperes.
 12. The method of claim 11 wherein step (b) comprises the step of: (f) flowing DC current of about 1000 amperes.
 13. The method of claim 1 wherein step (a) comprises: (d) maintaining the electrolyte wetting the surface at a temperature of no less than about 70 degrees Fahrenheit.
 14. The method of claim 13 wherein step (d) comprises the step of: (e) maintaining the electrolyte at a temperature of no less than about 150 degrees Fahrenheit.
 15. The method of claim 1 wherein step (b) comprises the step of: (d) continuously flowing the DC current through the body for not less than about 3 minutes and not more than about 30 minutes.
 16. The method of claim 1 wherein step (b) comprises the step of: (e) applying a DC voltage of between about 3 volts and 200 volts to the body while flowing the DC current through the body.
 17. The method of claim 1 comprising the step after step (c) of: (d) rinsing the surface with a low pressure water spray.
 18. The method of claim 17 wherein step (d) comprises the step of: (e) rinsing the surface no later than about 10 minutes after stopping the flow of DC current.
 19. The method of claim 1 wherein the body is a steel body, an aluminum body, an aluminum alloy body, a manganese body, a manganese alloy body, or a cast metal body.
 20. The method of claim 1 wherein the body has a surface coating to be cleaned from the surface, the method comprising the step of: (d) rinsing the surface coating off the surface with water after stopping the flow of DC current.
 21. The method of claim 20 wherein the surface coating is a powder coating.
 22. The method of claim 1 wherein the body is a wheel rim or a wheel hub of a motor vehicle.
 23. The method of claim 22 wherein the wheel rim or wheel hub comprises aluminum or an aluminum alloy.
 24. The method of claim 1 comprising the steps of: (d) sequentially cleaning a plurality of bodies in the electrolyte by performing steps (a), (b), and (c) for each body over a period of time; (e) maintaining the pH of the electrolyte greater than 7 for the entire period of time; and (f) maintaining the temperature of the electrolyte at or above 70 degrees Fahrenheit for the entire period of time.
 25. The method of claim 1 wherein step (a) comprises the step of: (d) immersing the body entirely or at least partially into the electrolyte.
 26. The method of claim 1 wherein step (a) comprises the step of: (d) spraying the electrolyte on the surface.
 27. The method of claim 1 comprising the steps of: (d) drying the body after cleaning, and then (e) coating the surface with a powder coating or other coating for reuse of the body. 